Are invasive apple snails important neglected decomposers of rice straw in paddy fields?

Abstract

Few studies have tested for the potential of invasive species, particularly pests, to contribute to ecosystem services. The apple snail Pomacea canaliculata is invasive in many countries around the globe. They are best known as pests of rice and great efforts are made by farmers to control the snails. However, apple snails might also act as decomposers of organic litter, and it was hypothesised that they might enhance the decomposition of rice straw. To test the ability of apple snails to feed on rice straw, choice and no choice feeding experiments were conducted offering rice straw to P. canaliculata for 2 weeks. As mature rice plants are not consumed by apple snails, the straw was incubated in water for 5 days and in water with a mixture of microorganisms for 25, 50 and 75 days prior to the feeding experiments. Rice straw of all treatments was consumed by snails without preference (11.6% more weight loss on average compared to controls in which snails had no access). In another experiment, snails were fed on rice straw for 6 weeks; body mass of snails was measured weekly. In treatments where access to straw was not restricted, all snails survived and body mass remained constant, whereas if access was restricted, snails lost body mass slightly. It was concluded that rice straw served as an alternative food for apple snails. Invasive apple snails spared in times when rice plants are not vulnerable could accelerate nutrient release from rice straw providing a benefit for farmers.